Acoustic diaphragm



sept. 1, 192s. 1,552,311

G. D. KELLOGG ACOUSTIC DIAPHRAGM Filed June 8I 1922 specifica-tion.

Patented Sept. l, 1925.

- UNITED STATES GEORGE D. KELLOGG, 0F lAIIBAINY,'IEI'E\ YORK.

AcoUs'rrc nIAPHnAeM.

Application med June 8, 1922. Serial No. 566,844.

To all whom t may concern.'

Be it known that I, GEORGE D. KnLmGc,'a citizen of the United States, residing at Albany, in the county of Albany and State of New York, have invented new and useful Improvements which the following is a specification.

Reference may be had to the accompanying drawings, and the reference characters marked thereon, which form a part of this Similar characters refer to similar parts in the several figures therein.

The principal object of the invention is to obtain more faithful recordin and more faithful and pleasing repro uctions of sounds.

Other objects will' appear in connection with the following description.

, Acoustic diaphragms, such as those used in sound-boxes, phonographs and the like,

have been made of various materials varying somewhat in elasticity and resiliency, but in all of which, so far as I am aware, the diaphragmwas inherently ca able of substantially free or undamped vibration upon the termination of the vibrational impulse.

A more faithful and pleasing reproduction of recorded sounds can be obtained by damping the vibrations of the diaphragm. This result I attribute to the fact that Where the diaphragm is inherently capable of substantially free and undamped vibration, a single vibrationaly impulse imparted to the diaphragm causes it to vibrate a number of times after that impulse is terminated-,-

the rst few ofthe successive vibrations being of almost the same amplitude and soundproducing force as the original vibration, the result of which, in a phonograph or the like, is that a second vibrative impulse is imparted to the diaphragm while it is still under the sound-reproducing vibrational iniuen'ce of the immediately preceding, but terminated, vibrational impulse.

Undamped sound-producing vibrations set u p-in such a diaphragm/by successive vibrative impulses thus overlap, interfere with,

and modify one another.

In carrying Vout my invention, I employ a diaphragm inherently capable ofdamped vibrations only, by which I mean that while the diaphragm is responsive to a vibrative impulse, the vibrations due to thatimpulse cease or become negligible as to producing, the production of, sound,

in Acoustic Diaphragms, off as soft .filler to so modify approximately as soon as that impulse is terminated. p

The results of man experiments have shown that it is desirabe to use in an acous-v tic diaphragm a soft elastic substance, s/ucli vulcanized rubber; and that, by bining with this elastic substance suitable adulterants or fillers, the resultant body can be made inherently capable of damped vibrations only, and can' -thus be made to accomplish the object of my invention.

For certain purposes of the invention, however, it is not necessary to use rubber; and good results can be obtained by the use of various other soft elastic substances such as gutta-percha, ber substltute.

By reclaimed rubber, I mean rubber which has been vulcanized and thereafter devulcanized so far as practicable. s

By rubber substitute, I mean any of the synthetic rubber compounds which are employed in place of soft vulcanized rubber. These are @usually made from oxidized oils, suchV as linse'ed oil, cottonseel oil, or other vegetable oils, acted upon either by chlorid of sulfur", or by sulfur boiled with the oil at a hi hv temperature. Such compounds are well own in the art, and further description of the same is deemed unnecessary.

Whatever highly elastic substance is employed in lcarrying out my invention, I add thereto a sufficient quantity of adulterant or and control the elastic substance that the diaphragm made from the product is inherently capable of damped vibrations only.

The nature and character of the adulterreclaimcd rubber, or rubant or filler can be varied inthe treatment^ of various elastic the desired result.

Certain adulterants or fillers suitablevfor this purpose are, asphalt or other bituminous substance, litharge,.and Whiting; and these may be combined with the selected elastic material in suchproportions as will bring about the desired result.

In combining an. elastic material with a filler or adulterant as above set forth, it is desirable to cure or vulcanize the mixture, and for this urpose to add a small amount of sulfur to t e mixture.

I have produced a highly satisfactory acoustic dia hragm embodying my invention by emp oying a mixture of crude rubsubstances to bring about ber, reclaimed rubber, asphalt, litharge, whiting; and sulfur in the fo lowing proportions: Crude rubber 5 per cent, reclaimedv rubber per cent, asphalt 10 per cent, litharge 5 per cent, whitlng 33 per cent, sulfur 2 per cent.

The method of manufacture is as follows:

The ingredients are mixed inY a mixing machine such as is commonly used in the manufacture of rubber compounds, and when thoroughly mixed are laced in a calendering machine and rolle into sheets of the desired thickness. The sheets are then vulcanized or cured to the desired degree.

The vulcanization can be accomplished by any known method, and preferabl in the manner in which soft vulcanized ru ber products are produced.

Diaphragms of the desired size and form can be cut from these vulcanized sheets and used in sound-boxes and the like, in which they may be mounted in any known manner.

`While a diaphragm made as above described may be used with good results, I prefer to incorporate in the diaphragm, a supporting body of fibrous material.

For certain urposes of the invention such a supporting dy may be formed of cords of fibrous material in any known manner; but I prefer to employ the cords in the form of an interwoven fabric. I use the term interwoven in its broad sense as including interweaving by means of loops as in knitted fabric, a though I prefer to employ a fabric composed of warp and weft threads;

and I have found cotton sheeting weighing three to iive ounces per square yard to be suitable.

In making a diaphragm by the use of such a fabric the fabric is first subjected to the action of a friction-machine whereby its surfaces are opened up and roughened. The frictioned fabric is then impregnated with a compound such as that above described and the calendered sheets of the compound are then applied to both sides of the 'frictioned fabric, and closely associated therewith by passing the fabric and theY applied sheets through either a frictioning machine or a calender machine until the desired thickness is obtained. Y

As dia hragms of different thicknesses may be diesired for different purposes, as many of the calendered sheets as necessary may be applied to the respective sides of the fabric to obtain the desired thickness. The fabric with the applied calendered sheets is then vulcanized into a unitary body.

If preferred, the mixture of ingredients above described can be dissolved in a solventV such as ether, gasoline or the like, and spread on the r ective sides of the frictloned fabric in thin layers, and the solvent allowed to evaporate; and successive layers may be of the invention.

thus applied until the desired thickness is obtained, after which the fabric with the applied material is vulcanized.'

Fig. l of the drawings is a cross-section of an acoustic diaphragm made in accordance with my invention, in the preferred manner above described.

. Fig. 2. is a similar view showing the diaphragm mounted in a sound-box suitable for use in a phonograph.

Fig. 3 is a similar view of a diaphragm made in accordance with my invention without the use of the sheet of fabric. l

Referring to Figs. 1 and 2 of the drawings, 1 is the sheet of fabric, and 2 is the material vulcanized upon the sheet of fabric as above described.

The diaphragm rests upon an annular shelf or flange, 3, within the sound-box and is held in position by a confining or clamping ring, 4.

The stylus-bar, 5, of the sound-box may be connected with the diaphragm in any known manner, but I prefer to have the stylus-bar formed with a head, 6, which has only simple Contact with the diaphragm.

I prefer to mount the diaphragm in the sound-box without Astraining or stretching the diaphragm, whereby the elastic material in the diaphragm is free from strain except that due to acoustic action.

With adiaphragm of this character, practically all of the force of the impulse transmitted to the diaphragm by the stylus-bar is converted into vibrational movement of the diaphragm, and little or none ofsuch force is used or lost in stretching the diaphragm.

This results in the vibrations being distributed over practically the whole surface of the diaphragm, and not localized at the point of contact of the head of the stylusbar with the diaphragm, as is the tendency in thepcase of elastic diaphragms made of stretched elastic material, or material inherently capable of substantially undamped vibration.

In Fig. 3 I have shown a diaphragm made in accordance with my invention without the use of the sheet of fabric. I do not wish to be limited to any particular elastic substance or any particular filler to be used therewith in carrying out my invention broadly, as various well known equivalents for the substances above particularly specilied may be employed for certain purposes l From numerous experiments and tests, it appearsthat, when the elastic substance has been so modified by combination with a suitable adulterant or filler that the modulus of resilience ofthe vulcanized product is less than one-half that of substantially pure soft vulcanized Par rubber, certain of the objects of my' invention can be accomplished Par rubber,

by the use of suc diaphragm.4V f

These tests have also apparently shown that vulcanized compounds suitable'for carrying out my invent1on respond in asimilar manner both to tests as to the modulus of resilience, and to tests made by the use of Shores scleroscope in which the material is tested by the rebound of a pellet or shot falling thereupon from a given height; .and I have thus found that vulcanized substances in which the elastic material has been so modified by an adulterant or filler that the rebound of the pellet in such a testing machine is less than half that of its rebound from substantially pure soft vulcanized are adapted for carrying out product in an acoustic my invention;

By whatever method the test is made, however, it appears that the soft vulcanized material suitable for carrying out my invention, has lessothan one-half the resiliency of substantially pure soft vulcanized Para rubber.

I have also ascertained by tests that diaphragms made as above described produce highly satisfactory results when the combination of the rubber or other highly elastic substance and filler is such that theyr together have an elongation at the point of rupture less than one-third that of substantially pure soft vulcanized ParJ rubber, o1' when the elongation of a testing piece three inches or less long, one inch or less wide and ratio of width to thickness less than ten, shall at the point of rupture be less than two hundred fifty per cent.

What Isclaim as new and desire to secure by Letters Patent is 1. A sound-box having a non-resonant acoustic diaphragm containing a highly elastic substance and a filler combined by chemical reaction, said diaphragm being supported within the sound-box without strain uponv the elastic material except that due to acoustic action.

sound-box having a non-resonant acoustic diaphragm containing semi-soft vulcanized rubber free from strain except that due to acoustic action.-

3. A `sound-box having a non-resonant acoustic diaphragm containing semi-soft vulcanized rubber, anda filler, said diaphragmbeingsupported within the soundbox without strain upon the elastic material except that due to acoustic action. 4. A simple, semi-soft, non-resonant acoustic diaphragm for sound-boxes containing an elastic substance and an inelastic substance united by chemical reaction free of strain or tension and inherently capable of damped vibrations only.

5. -A simple, semi-soft, non-resonant acoustic' diaphragm for sound-boxes containing y rubber, and a flller vulcanized, free of strain b or tension and inherently capable of damped vibrations only.

An acoustic diaphragm for soundboxes comprising a. non-resonant fabricsupported homogeneous` body the preponderant portion containing an elastic substance free of stra-in or tension and an inelastic substance and inherently capable of damped vibrations only.

acoustic diaphragm for soundboxes comprising4 a sheet of non-resonant woven fabric having mounted thereupon a preponderant homogeneous body containing a highly elastic substance and an inelastic substance free of Strain or tension whereby the vibrations of the elastic substance are damped. f

8. An acoustic diaphragm for soundboxes containing a highly elastic non-resonant substance and a filler free of strainvor tension, elastic substance and :filler united by chemical reaction having a resilience less than one-half that of substantially pure soft vulcanized Para rubber.

9. An acoustic diaphragm for soundboxes having incorporated therein a homogeneous non-resonant body of rubber and a. filler, vulcanized together and having a resilience less than one-half that of Substantially pure soft vulcanized Para rubber.

10. A sound-box having a non-resonant acoustic diaphragm comprising a fabricsupported body the preponderant portion containing a homogeneous body of highly elastic substance and a filler, said diaphragm being supported within the soundbox without strain upon the elastic material except that due to acoustic action. 11. A sound-box having a 'non-resonant 'acoustic diaphragm comprising a fabricsupported body the preponderant portion containing a homogeneous material of semisoft vulcanized rubber and a filler, said diaphragm being supported within the soundbox without strain or tension lupon the rubr except that due to acoustic action.

acoustic diaphragm for .soundboxes containing a vhomogeneous non-resonant body of highly elastic substance and a: filler, together having an elongation at the point of rupture less than one-third that of suptantially pure soft vulcanized Para ru er.

13. An 4acoustic diaphragm for sound- -I boxes having incorporated therein' a nonresonant homogeneous body of rubber and a filler -free of tension or strain, said rubber and filler united by chemical reaction and havin an elongation at the point of rupture less t an one-third that of substantially pure soft vulcanized Para rubber.

14. An acoustic diaphra for soundboxes containing a prepon erant homo nons non-resonant e astio substance an a ituminous substance. f

/ 15. An elastic diaphragm for soundboxes containing a homogeneous non-resonant body of elastic rubber and asphalt.

16. .An acoustic diaphragm for soundboXes containing non-resonant rubber, a filler and sulphur vulcanized together into a homogeneous soft body having less than one-half the resiliency of substantially pure soft vulcanized Para rubber.

17. An acousticv diaphragm for soundboxes containing non-resonant rubber, a liller and sulphur vulcanized together into a homogeneous soft elastic body free of strain or tension and having an elongation at the point of ru ture less than one-third that of substantia ly pure soft vulcanized Par rubber. A

18. An acousticf diaphragm for. soundboXes containing a homogeneousbody of non-resonant rubber and a filler vulcanized together free of strain or tension and in such proportions that the elongation of a test piece three inches or less long, one inch or less Wide, and ratio of Width to thickness less than ten, shall at the point of rupture be less than two hundred fifty per cent.

19. A diaphragm for sound-boxes containing a. preponderant homogeneous nonresonant body of soft vulcanized elastic man terial and a filler free of strain and having less than one-half the resilience of substantially pure soft vulcanized Para rubber.

20. An acoustic diaphragm for soundboxes containing a homogeneous soft elastic body free of strain and formed of crude rubber, reclaimed rubber, asphalt, lit-harge, Whitin and 'sulphur vulcanized together.

21. 11 acoustic diaphragm or soundboxes having incorporated therein a homogeneous body of non-resonant soft elastic material and filler of less than one-half the resiliency of substantially pure-soit vulcanized Par rubber.

In testimony whereof, I have hereunto set my hand this 6th day of June, 1922.

GEORGE D. KELLOGG. 

